Atomic-scale structure of RCo2 (R[dbnd]Tb,Dy) compounds studied by X-ray diffraction and pair distribution function analysis

Abstract

The RCo2 compounds have attracted lots of research interests due to the giant magnetostriction effect. The average structure of these compounds have been well established, but the studies on the local structure are still rare. In this paper, the average structure and the local structure of the RCo2 (RTb, Dy) compounds were investigated with a combination of X-ray diffraction (XRD) and pair distribution function (PDF) analysis, and the electronic structure were studied by the first principle calculations. The results demonstrate that these two compounds present MgCu2-type cubic structure at both average and local scale at room temperature. The variation of the R–Co bond length is much larger than that of the Co–Co bond length with changing R element. The Co–Co bond of TbCo2 compound shows abnormal change around the structural transition. The hybridization between R-5d state and Co-3d state strongly affect the R–Co bond, while the magnetic polarization of Co-3d state show stronger effect on the Co–Co bond. These findings highlight the important role of atomic-scale structure in determining the magnetic properties of the RCo2 materials.